Your router has an internal firewall.
If the router supports UPnP, enable it & then choose the UPnP option within LW's tools > options > advanced > firewall config. If that doesn't help, you could try port forwarding. There are instructions for your router below
http://www.portforward.com/english/r...1/Limewire.htm

Don't forget to set up a static IP first, you'll find instructions within the port forwarding guide. Remember that LW's listening port & the port forwarded must be the same number

You could also try reconfiguring your Norton firewall if neither of those suggestions works.